Pneumatic valve springs

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Pneumatic valve springs are metal bellows filled with compressed air^[1] occupying roughly the same space of metal springs used to close valves in high-speed internal combustion engines. This system was introduced in the mid-1980s in Renault turbocharged 1.5 litre Formula 1 engines.

Reducing the number of moving parts that can fail is good engineering. Racing engines often failed at high speeds because mechanical springs were unable to close valves fast enough, leading to engine failure when pistons struck incompletely closed valves. Renault's innovation was to replace steel springs with light weight compressed air bellows that could respond more quickly and reduce the possibility of valve crashes, other than from leaking bellows. Additionally, the amount of seat tension required to keep a coil sprung valve under control results in peak lift loading drastically higher, with added stress to the entire valvetrain as a result. Pneumatic systems, sharing a common reservoir of pressure retain a more static level of force, controlling the valve effectively, without any attendant peak lift load increase. To avoid bellows failures, air springs are replaced often.

Pneumatic valve springs gave Renault an advantage with its turbocharged engines, often said to be the most powerful. However, reliability and poor handling of their chassis kept the cars from success until 1989 when Renault provided Williams with its V10 engine to begin a winning streak. Renault won the constructors' championship with Williams in 1992, 1993, 1994, 1996 and 1997, and with Benetton in 1995. Nigel Mansell, Alain Prost, Michael Schumacher, Damon Hill and Jacques Villeneuve each won a Driver's championship in the 1990s with Renault engines.

While pneumatic valve springs have become standard in Formula 1 engines, Renault has been researching computer controlled electro hydraulic valves using no camshaft, to reduce moving parts while improving valve control.

Pneumatic valve springs are also found in several Moto GP motorcycle engines.